48 



NA TURE 



\jSIov. 19, 1874 



The Cry of the Common Frog 



In Nature, vol. x. p. 461, Mr. Mott notices the cry of the 

 common frog when annoyed. One of the greatest enenues of 

 this frog in the United States is the common striped snake 

 (Ti opidonotus hr?iia, Dekay). He seizes the frog by the liind 

 legs for the purpose of swallowing him, when the latter will 

 utter a most pitiful cry. I have detected them in this condition 

 at a distance by the frog's note. I have amused myself by 

 taking a frog by the hind legs and dragging him slowly bick- 

 wards on tlie ground in a serpentine direction, when lie will 

 exhibit his charac'eristic wail to perfection ; and, when released, 

 he will frequently utter some apparently intelligent imprecations 

 as he hops off out of reach. I have noticed the same effect pro- 

 duced by a playful kitten amusing itself by teasing the frog, seem- 

 ingly for the purpose of hearing him cry. Sliding a .stick after 

 him like a snake will produce the same results in a still more 

 striking manner. A. T. T. 



Oswego, U.S., Oct. 29 



Phylloxera Vastatrix 

 Can any of your readers kindly inform me where a specimen 

 of Phylloxera vastatrix can be obtained ? 



Ipswich A. Harwood 



A Nest of Young Fish 



While on the point of taking my accustomed morning plunge 

 in one of the clear pebbly streams that find their way into the 

 plains from the northern mounta n ranges of the island of 

 Trinidad, my attention was attracted by the eccentric movements 

 of a small fish of the peich tribe. In general this fish is extremely 

 shy, scudding off into deep water or under some ovei hanging 

 bank on the approach of man ; on this occasion, however, on 

 putting my hand into the water, the fish, to my astonishment, 

 darted forward again and again, striking my hand with consider- 

 able force. Rather at a loss to account for such temerity in a fish 

 only 4 in. long, I watched its movements narrowly, and at last 

 found out the cause. In a small hollow close by, about the size 

 of half an egg, artistically excavated from the bright quartz sand, 

 a multitude of tiny fish were huddled together, their minute fins 

 and tails in constant motion. They had apparently been or.ly 

 very recently hatched, and were no larger than common house 

 flies ; the parent fish kept jealous watch over her progeny, 

 resenting any attempt on my part to touch them. 



Next morning, accompanied by my father and bro hers, I 

 returned to the spot which I had carefully maiked the day 

 before. For some time, however, we searched in vain for the 

 fish and her young ; at length, a few yards further up stream, 

 we discovered the piarent guarding her fiy with zealous cate in a 

 cavity similarly scooped out of the coarse sand ; any atteoipt to 

 introduce one's finger into the hollow was vigorously opi o eJ by 

 the watchful mother. This is the fiist and only instance that has 

 come under my notice of a fish watching over her young, ani 

 conveyirg them, when threatened by danger, to some other 

 place, 'ihe clear streams that flow along the vaileys among 

 the northern mountain ranges of the island abound with fish of 

 the variety I refer to ; they are in general of a bright yellowish 

 brown, with two or more silvery stripes on the sides, and seldom 

 exceed five inches in length ; but in the sluggish turbid rivers of 

 the plains, the bright colours change to a dull brown ; the fish 

 are larger, however, varying in size from eight to ten iiichis. 

 E.xtremely tenacious of life, these fish, in common with several 

 other species, have the power of existing in a semi-torpid state 

 for weeks, and even months, buried during severe droughts in 

 the mud of dry watercourses, where they aie dug up by the 

 Creole peasants, who prize them as food ; but from the peculiar 

 earthy ilavour common to many \arieties of freshwater fish fre- 

 qutming the muddy rivers of the low lands, they are not relished 

 by the more fastidious pala'e of the European. 



■ Robert W. S. Mitchell 



THE DEVELOPMENT OF MOLLUSC A 



MR. RAY LANKESTER, in the current number of 

 the Quarterly Journal of Microscopical Science, 

 gives the results of his examination of the embryo of the 



cotnmon Pond Snail {Liniiiccus stagiialis.') These are of 

 great importance; first, because they show how much may 

 be done by trained observation, with improved methods, 

 of a very common form, which has already been studied 

 by excellent anatomists,; and secondly, because Mr. 

 Lankestei's previous investigations into the develop- 

 ment of cuttles, Pisiiliii})!,^T\d several marine gasteropods, 

 enable him to form a sound judgment of the bearing 

 of his discoveries upon questions of homology and of 

 classification. 



In Limnreus, Mr. Lankester finds that the process of 

 segmentation (which is well illustrated by drawings of 

 the egg in various pnsitions at the several stages) is fol- 

 lowed by the formation of a gastrula through a process of 

 invagination. This gastrula (for Mr. Lankester adopts this 

 term from Prof. Ha-ckel instead of " planula," the one he 

 himself invented), with its double layer of cells and single 

 orifice, develops into the next stage by the mouth closing 

 and afterwards giving rise to the anus, while a fresh oral 

 opening appears and a velum is developed. The presence 

 of a veluiTi in pulmonate Gasteropoda has not, we believe, 

 been previously established, and is of great morphologi- 

 cal importance. It is, Mr. Lankester believes, homo- 

 logous with the trochal disc of rotifers, and he proposes 

 the term "veliger" for the phase of development in 

 which it appears. Nay, he gives reasons for regarding 

 the subtentacular lobes of the adult Lymna-us as a residue 

 of the velum. If it be so, it is the only instance jet 

 known of this embryonic structure persisting in the per- 

 fect form. 



The " anal cone " of M. Lereboullet is shown to have 

 nothing to do with the anus, which is developed in the 

 pedicle left by the obliterated gastrula-mouth. The 

 functional import of the "anal-cone," or rather gland-sac, 

 is still obscure. It has been already recognised by Mr. 

 Lankester in Pisidiitm, Ap'n'sia, and Ncrctina, and by 

 Hermann Fol in einbryo Pteropoda. It is possibly homo- 

 logous with the basal gland described by Keferstein 

 and Kowalevsky in Loxosonia among Bryozoa, and with 

 a similar structure in Tcrcbratula. The more diffi- 

 cult questions of its homogeny with the rudiinentary 

 internal shell of the slug, and with the pen- 

 sac of cuttles, are also discussed. One of the most 

 curious facts about this "shell-gland" is that it frequently 

 becoines irlled with a homogeneous refracting secretion 

 apparently chitinous in composition, which is a morbid, 

 or at least an abnormal change, and associated with 

 irregular development of the embryo. 



Not the least valuable point established in this interest- 

 ing memoir is that the rotation of the embryo Lymnjeus is 

 caused by numerous short cilia on the annular band 

 whic'a afterwards fonns the velum. The discovery of 

 these cilia, which were sought by Lereboullet without 

 success, is probably due to IMr. Lankester having used 

 ptrcsmic acid, a reagent which is exceedingly useful in 

 examining transparent Tunicata, and seems equally suited 

 for displaying cilia anywhere. 



The gastrula form appears apparently in all groups of 

 animals but the highest and the lowest, in some form or 

 other ; but the " shell-gland " forms a valuable additional 

 link between the Erachiopoda and Polyzoa on the one 

 hand and the higher Molluscs on the other. If this be ad- 

 mitted, it is probable that Tunicata may be again admitted 

 to the same great stem in spite of their undoubted affi- 

 nities to vertebrates by Anipliioxys, and to worms by 

 Balanoglossiis. 



It is a most satisfactory sign of the revival of embry- 

 ology in England, that in the same number of the Quar- 

 terly Microscopical yo?irnal \\h.\ch. contains this important 

 memoir by Mr. Lankester, there is also the preliminary 

 account of the development of Elasmobranchii, by Mr. 

 Balfour, which excited so much interest at the late meet- 

 ing of the British Association. 



